The present invention relates to a rotary printing press for additional printing, for example, of serial numbers, the press having an inspection apparatus for checking printed products for acceptability prior to additional printing operations.
To meet a wide variety of printing requirements in recent years, there has been an increasing demand for printed products or sheets which include images or patterns previously printed and various additional marks or indicia such as serial numbers, seals and stamps, store names and management codes, that are subsequently printed. Such printed products are often produced successively by a printing press for printing images and another printing press coupled therewith for printing marks or numbers. Alternatively, products on which images have been printed are supplied to an independent printing press for the printing of indicia or other additional information. Printed sheets which require such additional printing include bank bills, securities and fancy art prints that are individually important or expensive. These are printed in separate processes for printing patterns and for printing additional marks, numbers or characters, respectively. The prints on which patterns have been printed are checked for defects prior to the additional printing operation. Only those prints which have an accepted quality of printed images are allowed to go to press for additional printing, thus avoiding the production of defective printed products. Those printed products which need to be serially numbered with no missing number allowed, such as bank bills, are required to undergo a stringent inspection for any flaws before other marking are additionally printed on the prints. The conventional inspection and selection practice has relied on checking apparatus installed in a wide area and attended by inspectors for visual inspection. In order to enable the inspection process to keep up with the high-speed printing operation, a large number of skilled inspectors would be required, an expensive prospect which would lead to many problems.
Recent progress in electronics and optical equipment has resulted in the development of an apparatus for electrically detecting non-printed sheets, sheets printed out of registry, doubling, improper and uneven print densities, and other defects through an optical system, and for producing electrical output signals indicative of whether printed products inspected are acceptable or not, such inspection occurring at speeds comparable to high speeds of operation of printing presses. Since the inspection process is carried out independently of the printing process, however, the above described apparatus still requires a large amount of manpower to take care of the inspection process, to deliver the printed sheets from the printing press for printing patterns to the inspection apparatus, to deliver the printed sheets from the inspection apparatus to an additional printing press, and to stack them in place. Therefore, the prior art inspection apparatus does not save labor and, hence, reduce the cost of printing, and cannot be operated to full advantage.